This invention relates to the detection of wood boring insects, and in particular to the use of contact sex pheromones in the detection and identification of the Emerald Ash Borer (EAB) Agrilus planipennis Fairmaire (Coleoptra: Buprestidae).
The waxy layer on the cuticle of insects provides a hydrophobic barrier that prevents desiccation and may also provide patterns for mimicry or camouflage, repel excess rainwater, reflect solar radiation, and give species-specific olfactory cues. Some of the hydrocarbon components also function as contact pheromones. There is good evidence that in the Cerambycidae, mate recognition is mediated by contact chemoreception with this waxy layer wherein males orient to females only after antennal contact with the cuticle of a female (live or freeze-killed) with subsequent copulatory behavior and coupling to the females' genitalia (Ginzel et al. 20031). The reference also discloses a female cuticular hydrocarbon extract containing 9-methylpentacosane, as a contact pheromone for Xylotrehus colanus (Coleoptra: Cerambycidae). Whether or not contact chemoreception is important in the Buprestidae such as the EAB, is unknown.
The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive buprestid species originating from Asia that has caused extensive mortality of ash trees (Fraxinus spp. L.) (Oleaceae) since its introduction into the USA and Canada (Haack et al. 20022;) and its continued spread in North America threatens all native ash species. Movement of infested firewood and nursery stock has exacerbated the natural spread of EAB and large-scale devastation of ash trees has occurred in both urban and rural environments. Monitoring of this rapid spread has proven challenging because it is very difficult to detect low to moderate densities of EAB using visual surveys, and evidence to date suggests that EAB use visual cues rather than pheromones to locate mates (Otis et al. 20053; Rodriguez-Soana et al. 20064; Lelito et al. 20075, 20086). Trap trees, consisting of girdled ash trees with sticky bands, have detected new outlier EAB infestations but they are labor intensive. Purple-colored sticky traps catch EAB better than any other color tested (Francese et al. 20057), particularly when these traps are baited with host volatiles, either sesquiterpenes found in ash bark (Crook et al. 20088) or ash leaf volatiles (Rodriguez-Soana et al. 20064; de Groot et al. 20089). Although an antennally active compound emitted primarily by female EAB has been identified (Bartelt et al. 200710), its biological activity has yet to be demonstrated. Improved detection methods and management tools are urgently required but there is a paucity of information on the chemical ecology of this insect.
The mating biology of the EAB is poorly understood. For other buprestids, it has been suggested that individuals locate a susceptible host and then search for mates using visual and tactile cues. (Dunn and Potter 198811) observed greater catches of male twolined chestnut borer, Agrilus bilineatus (Weber), in cages containing conspecific females than in empty cages, and suggested the attraction could be due either to a pheromone or to auditory cues produced by the females. Visual cues have clearly been demonstrated to be important in orienting EAB males to potential mates (Otis et al. 20053; Lelito et al. 20075, 20086). Dead EAB adults of either sex, whether they had been washed in solvent or not, elicited the same number of approaches by feral male EAB; in addition, males spent comparatively more time investigating unwashed females than males or washed females, suggesting the presence of a contact pheromone on the cuticle of female EAB (Lelito et al. 20075). The identity or chemical composition of this putative contact pheromone was not determined.
Information on the identity and biological activity of an EAB contact pheromone would increase our understanding of the mating ecology of this and other buprestid species.